1. Field of the Invention
The present invention relates to a method for manufacturing ink jet recording heads. More particularly, the invention relates to a method for manufacturing ink jet recording heads, that is capable of setting the ink-discharge, pressure-generating elements and the ink-discharge openings (ports) of each head with extremely high precision in a shorter distance with a good reproducibility to record images in higher quality without any deformation of the head due to the applied heat, while providing a good resistance to ink and erosion, as well as a higher dimensional precision and reliability that may be affected otherwise by swelling or the like.
2. Related Background Art
An ink jet recording head applicable to the ink jet recording method (liquid jet recording method) is generally provided with fine recording-liquid discharge openings (ports), liquid-flow paths, and liquid-discharge, energy-generating portions, each arranged on a part of each liquid-flow path. Then, to obtain high quality images using an ink jet recording head of this kind, it is desirable to discharge small droplets of the recording liquid from the respective discharge openings (ports) each in an equal volume always at the same discharge speed. In this respect, there has been disclosed in the specifications of Japanese Patent Application Laid-Open Nos. 4-10940 to 4-10942, a method for discharging ink droplets in such a manner that driving signals are applied to the ink-discharge pressure-generating elements (electrothermal transducing elements) in accordance with recording information to cause the electrothermal transducing elements to generate thermal energy, which provided a rapid temperature rise to ink beyond its nuclear boiling point, thus forming bubbles in the ink to discharge ink droplets by communicating these bubbles with the air outside.
As an ink jet recording head that may implement such method, it is preferable to make the distance between each of the electrothermal transducing elements and discharge openings (ports) (hereinafter referred to as the "OH distance") as small as possible. Also, for this method, the discharge volume is determined almost only by the OH distance. Therefore, it is necessary to set the OH distance exactly together with a good reproducibility.
Conventionally, as a method for manufacturing ink jet recording heads, there is a method such as disclosed in the specifications of Japanese Patent Application Laid-Open Nos. 57-208255, and 57-208256, wherein the nozzles formed by ink-flow paths and discharge openings (ports) are patterned by the use of photosensitive resin material on the substrate having ink-discharge, pressure-generating elements formed on it, and then, a glass plate or the like is bonded to cover the substrate, or a method such as disclosed in the specifications of Japanese Patent Application Laid-Open No. 61-154947, wherein the ink flow path pattern is formed by soluble resin, and this pattern is covered with epoxy resin or the like to harden it, and then, after the substrate is cut off, the pattern formed by the soluble resin is removed by elution. However, any one of these methods is arranged to be adoptable for manufacturing only an ink jet recording head whose discharge direction is different from (almost perpendicular to) the development direction of bubbles. Then, for a head of this type, it is arranged to set the distance between the ink-discharge, pressure generating elements and the discharge openings (ports) by cutting off each of the substrates. As a result, the cutting precision becomes an extremely important factor for controlling the distance between them. Since, however, the cutting is executed by the use of a dicing saw or some other mechanical means in general, it is difficult to carry out the setting performance with an extremely high precision.
Also, as a method for manufacturing an ink jet recording head whose type is such that the development direction of bubbles is almost the same as that of the discharges, there is a method disclosed in the specification of Japanese Patent Application Laid-Open No. 58-8658, wherein the substrate and the dry film that becomes the orifice plate are bonded through the other patterned dry film, and then, the discharge openings (ports) are formed by means of photolithography, or a method disclosed in the specification of Japanese Patent Application Laid-Open No. 62-264975, wherein the substrate having the ink-discharge, pressure-generating elements formed on it and the orifice plate processed by electrolytic casting are bonded through dry film, among some others. Nevertheless, with any one of these methods, it is difficult to form the orifice plate thin uniformly (in a thickness of 20 .mu.m or less, for example), and even if such thin orifice plates can be produced, it becomes extremely difficult to execute the bonding process between the substrate having the ink-discharge, pressure-generating elements on it with the thin orifice plate due to its brittleness.
In order to solve these problems, there is disclosed in Japanese Patent Application Laid-Open No. 6-286149 a method for manufacturing ink jet recording heads that is capable of setting the ink-discharge, pressure-generating elements and the discharge openings (ports) with a short distance in an extremely high precision and with a good reproducibility to record images in higher quality with such a manner that (1) after ink-flow paths are formed by the patterning by use of soluble resin on the substrate having ink-discharge, pressure-generating elements on it, (2) the solid epoxy resin containing coating resin in it is dissolved in a solvent at room temperature, which is coated on the soluble resin layer by the application of solvent coating to form the covering resin layer that may become ink-flow path walls on the soluble resin layer, and then, (3) after the ink-discharge openings (ports) are formed on the covering resin layer above the ink-discharge, pressure-generating elements, (4) the soluble resin layer is eluted for the provision of the aforesaid ink jet recording head. With this method, it is possible to shorten the processes of manufacture and obtain an inexpensive but reliable ink jet recording head.
Nevertheless, there are still problems given below for the method disclosed in the specification of Japanese Patent Application Laid-Open No. 6-286149.
(1) Since the ink-flow-path walls are usually formed with resin on the silicon substrate, deformation tends to take place due to the difference in linear expansion factors of the inorganic material and resin. As a result, a problem is encountered with respect to the mechanical characteristics of the walls thus formed. PA1 (2) The edge portion of resin formation is often rounded. Then, the sharpness of the resultant edge thereof is often insufficient. In some cases, therefore, the dimensional precision obtained is not necessarily good enough. PA1 (3) Resin is subjected to swelling and easy peeling off. In some cases, therefore, its reliability is not necessarily good enough.